Not Applicable
This invention relates generally to a hypodermic needle that is useful for applying a local anesthetic to block nerve transmission, otherwise known as regional anesthesia or any intramuscular injection of medications requiring skin penetration.
The somatic senses are the nervous system mechanisms that collect sensory information throughout the body. They are classified into three different physiological types: (1) the mechanoreceptive somatic senses, stimulated by the mechanical displacement of some tissue of the body, (2) the thermoreceptive senses, which detect heat and cold, and (3) the chemoreceptive senses, which are activated by excess hydrogen ion (i.e., an acidic environment). There are at least six different types of tactile receptors known, but many more similar ones also exist. Some examples are free nerve endings, which are found everywhere in the skin and many other tissues; Meissners corpuscles, encapsulated nerve endings that excite a large (type AB) myelinated sensory nerve fiber; Merkels discs and Iggo dome receptors which project upward against the underside of the epithelium of the skin; Pacimian corpuscles which are deeper in the skin tissue of the body for detecting vibration or other changes in mechanical positioning. When activated, these receptors send neurochemical signals to the brain to be processed and acted upon in response to a stimulus.
Pain is a protective mechanism for the body. It occurs whenever any tissues are being damaged, and it causes the individual to react by moving away from the pain stimulus. The pain receptors in the skin and other tissues are mainly free nerve endings. They are widespread in superficial layers of the skin and also in certain internal tissues, such as the periosteum, the arterial walls, the joint surfaces, and the falx and tentorium of the cranial vault. Most of the other deep tissues are not extensively supplied with pain endings but are sparsely supplied, but, nevertheless, any widespread tissue damage can still summate to cause an aching type of pain in these areas. Therefore, anything that is deposited under the dermal layer causing distension will be sensed by receptors and will be activated according to its specificity.
There are many factors that can elicit injection pain such as temperature of the injected solution, the acidity of the solution, and the mechanical method of injecting, such as the speed and the local delivery of the fluid to a specified location, causing distension. These challenges to painless injection have been studied and many new methods of injection have been devised to lessen injection pain. For example, the temperature of the solution challenge can be overcome by warming the injected solution to 37 degrees Celsius, which will substantially reduce pain as described by Fletcher, G. C. et al., in xe2x80x9cThe effect of temperature upon pain during injection of propofol,xe2x80x9d Anesthesia, May 1996, 51(5):489-9. The acidic nature of the injected solution often needed for storage can cause significant post injection pain. For example, lidocaine is often used for skin anesthesia and causes severe sharp pain post-injection in the dermal wound due to its high acidity. One solution is to increase the pH of the lidocaine by diluting the lidocaine with sodium bicarbonate, a base solution, which will decrease the hydrogen ion concentration to a normal body pH, thus decreasing the amount of acid (H+) ions irritating the chemoreptors. This was extensively explained in research papers by Parham, S. M. et al., entitled xe2x80x9cEffect of pH modification by bicarbonate on pain after subcutaneous injection,xe2x80x9d Can. J. Surgery, Febauary 1996, 39(1):31-5 and Palmon, S. C. et al., entitled xe2x80x9cThe effect of needle gauge and lidocaine pH on pain during intradermal injectionxe2x80x9d Anesth. Analg. February 1998, 86(2):379-81. Both papers pointed out the significant decrease in pain associated with the intradermal injection of lidocaine mixed with bicarbonate. Also, in the last paper, Palmon et al. also demonstrated that changing needle size from 25 G to 30 G did not affect the injection pain by any significant amount.
The factor of mechanical tissue distension in the area surrounding an injection site stimulating mechanosensitive pain receptors has been well studied but has not yet been challenged. When activated, these receptors transduce pain via the fast mechanico C-pain fibers that induce a severe pain sensation. The pain sensations caused by tissue distension tell the body of impending injury. This effect was observed by Jorgensen, J. T. et al. and reported in xe2x80x9cPain assessment of subcutaneous injections,xe2x80x9d Ann. Pharmacotherapy, July-August 1996, 30(7-8): 729-32 1996, and by Simone et al., and reported in xe2x80x9cDose-dependent pain and mechanical hyperalgesia in humans after intradermal injection of capsaicin,xe2x80x9d Pain 38(1989), 99-107 where it was observed that even a minimal injection change from 0.5 mL to 1.0 mL will significantly increase local pain in the injected area from distension. Also, these papers demonstrated that the distention resulted in additional mechanical hyperalgesia in the surrounding tissue that can last longer than twentyfour hours.
A modified conventional hypodermic needle, having a blade-like cutting edge tip for penetration of the flesh and lateral orifices through which anesthetic or other solution is ejected, can reduce pain. It has been theorized that during the process of injection, the painful stimulus that is felt by the patient during the injection is mechanical distension pain more so than pain associated with the action of the sharp needle piercing the skin. The actual tissue distension causes an activation of small delta type A fibers and mechanico C- pain receptors in the dermal and subcuticular layer throughout the body. The injected fluid displaces the nerve-ending fibers and thus causes activation of painful stimuli. The injected fluid causes local distension and therefore excites the mechano-sensitive pain receptors by causing mechanical stress or mechanical tissue damage. The mechanosensitive pain receptors are activated when mechanical stress or damage to the tissues is taking place. This was demonstrated in a study by Jorgensen, J. T. et al. in Demark which showed that there is a direct relationship between the pain of injection and the injection volume and that an increase of volume from 0.5 to 1.0 mL increases pain significantly.
The needle of the present invention, with its multi-perforated lateral holes, decreases local tissue distention and reduces the activation of many nearby skin receptors, thus decreasing mechanical pain secondary to distension during and immediately after injection of fluids. By reducing the amount of pressure that is exerted on a certain distinctive area of skin by increasing the surface area of fluid diffusion, pain can theoretically be decreased. The needle has multiple perforated distal holes all located at the distal third of the needle length which allows it to evenly dispense the injected substance over a greater area while still remaining localized to a certain tissue depth. By decreasing the pressure via increasing the outflow area, there is less local distension and, therefore, a decrease in the number of nerve endings activated/stimulated. This phenomenon is described by Bernoulli""s principle that dictates the relationship between area and pressure. When an area is increased, the pressure decreases in accordance with the proportionality of the amount of fluid injected. Therefore, the patient in theory perceives less pain other variables being unchanged.
The hypodermic injection needle of the present invention has an elongated rigid shaft of a predetermined length which varies from 0.5 to 1.5 inches and a diameter which varies from 16 G to 28 G. The shaft includes a hollow, interior passage that terminates at the tip of the needle with precise honed-edge bevel design that easily penetrates tissue with an incision that minimizes trauma. One end of the needle is fastenable to a conventional syringe. Adjacent to the needle tip, multiple lateral perforated openings along the circumference of the shaft, which are about 0.02 inch in diameter, are spaced strategically such that the injection fluid can be dispensed at approximately a 90-degree angle to the longitudinal axis of the needle shaft.
The multiple perforated openings are such that the needle disperses the injected fluid over a larger area through the lateral facing elliptical orifices (relative to the needle shaft), greatly reducing the liquid pressure on the surrounding environment, therefore creating a decrease in displacement and a decrease in activation of pain receptors.
In the preferred embodiment, the improved needle has a sharply-honed tip opening followed by a plurality of elliptical orifices (0.2 inches wide) at a variable distance of no more than thirty percent of the total needle cannula. The orifice closest to the tip is placed immediately and longitudinally adjacent to the distal opening. Four orifices for achieving multiple openings in each needle may be located at 0.0313 inch intervals staggered around the needle circumference to minimize the destruction of the integrity of the needle, but not in the same axial plane as each other. These lateral openings are perpendicular to the axis of the needle shaft or can be placed at a 45-degree angle toward the distal tip as desired to decrease the amount of tissue blockage upon piercing skin. The needle gauge may be varied depending on the desired tissue depth and particular situation. The dimensions described herein for the preferred embodiment use a 22 Gxc3x97one-inch needle but all other needle sizes can be provided with proportionally-placed holes according to the size and gage of the needle in question.
The needle of the subject invention can be used in many situations that require injection through skin. The injection can be intramuscular, intradermal or subcuticular provided it requires a needle method. It can be used in dentistry for oral nerve blocks, for insulin injection in diabetic patients on a daily basis for blood sugar control, and for routine immunizations. The perforated distal holes can be easily applied to any presently-manufactured needle by means of a simple modification.
The needle can be of four specific designs. One is that of a regular straight shaft with perforated lateral holes according to the above description. The second variation is similar to the first except that the distal tip is closed and all fluid escapes from the lateral holes. The third design is that of a tapered needle (0.9 mm proximal to 0.3 mm distal) with lateral holes and an open distal tip. The fourth design is a tapered needle with lateral holes and a closed distal tip.
While the above description contains many specifics, these should not be construed as limitations of the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. Many other variations are possible. For example, the distal opening can be sealed leaving the lateral holes as the only path along which the injected solution can escape or the lateral holes can be made in different sizes ranging from larger to smaller and vice versa or at a different spacing.
Accordingly, the scope of the invention should be determined not by the embodiment(s) illustrated, but by the appended claims and their legal equivalents.
It-is the object of the present invention to provide an improved hypodermic needle for use with conventional syringes that reduces or eliminates pain by decreasing the injection pressure thereby reducing fluid distension and thus pain.
In accordance with these and other drawings that will be apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.